ConcepTest 26.1
Reflection
1) the Moon is very large
When watching the Moon over
the ocean, you often see a long
2) atmospheric conditions are
just right
streak of light on the surface of
3) the ocean is calm
the water. This occurs because:
4) the ocean is wavy
5) motion of the Moon
ConcepTest 26.1
Reflection
1) the Moon is very large
When watching the Moon over
the ocean, you often see a long
2) atmospheric conditions are
just right
streak of light on the surface of
3) the ocean is calm
the water. This occurs because:
4) the ocean is wavy
5) motion of the Moon
When the water surface changes, the angle of
incidence also changes. Thus, different spots
on the water can reflect the Moon into your
eyes at different times.
Follow-up: Where else does this occur?
ConcepTest 26.2a
Mirror I
mirror
An observer at point O is facing a
mirror and observes a light source
3
O
S. Where does the observer
perceive the mirror image of the
1
source to be located?
S
2
4
ConcepTest 26.2a
Mirror I
mirror
An observer at point O is facing a
mirror and observes a light source
3
O
S. Where does the observer
perceive the mirror image of the
1
source to be located?
S
2
Trace the light rays from the object
to the mirror to the eye. Since the
brain assumes that light travels in a
straight line, simply extend the rays
back behind the mirror to locate the
image.
Follow-up: What happens when the observer starts moving
toward the mirror?
4
ConcepTest 26.2b
You stand in front of a
mirror. How tall does the
mirror have to be so that
you can see yourself
entirely?
Mirror II
1) same as your height
2) less than your full height but
more than half your height
3) half your height
4) less than half your height
5) any size will do
ConcepTest 26.2b
You stand in front of a
mirror. How tall does the
mirror have to be so that
you can see yourself
entirely?
Mirror II
1) same as your height
2) less than your full height but
more than half your height
3) half your height
4) less than half your height
5) any size will do
Trace the light rays from the
image’s foot to the mirror and then
to the eye. Since we know that qi
= qr , you need a mirror only half
your size.
ConcepTest 26.2c
Mirror III
1) no
Does this depend on your
distance from the mirror?
2) yes
3) depends on the mirror
4) depends on the person
ConcepTest 26.2c
Mirror III
1) no
Does this depend on your
distance from the mirror?
2) yes
3) depends on the mirror
4) depends on the person
The further you step back, the
smaller the incident and
reflected angles will be. But the
rays will still be reflected at the
same points, so the ray from the
foot will still be reflected at midheight.